More than half, or 52%, of the 1,000 13- to 17-year-old children surveyed through revealed that they used lesson time to look at social networking sites, according to research carried out by IT security consultancy Global Secure Systems.
The study also found that more than 25% of the sample said they did so for more than 30 minutes a day.
David Hobson, the managing director of GSS, was alerted to the phenomenon when he was giving a talk on internet ethics and behaviour at a public school. During his presentation to the class of 13 year-olds, who were equipped with laptops, he asked how many had visited social networking sites during their lessons. The entire classroom raised their hands.
This discovery provoked Hobson into investigating further to see whether the practice was widespread.
He said: "Kids are potentially wasting as much as two and a half hours a week of lessons on Facebook."
"I recognise that there is a place for social networking, with a whole new generation now relying on it to communicate, but not at the expense of an education.
"Schools could learn a lesson from industry and ensure school children productively use the internet. Through the deployment of software, access to inappropriate websites can either be completely blocked, or limited to break time, economically and efficiently."
In a separate poll by GSS and Infosecurity Europe 2008, it was claimed that the recent popularity of social networking sites such as Facebook, and , is costing UK corporations close to £6.5bn annually in lost productivity.